To meet the continued fast growing demand of mobile data, the wireless industry needs solutions that can provide very high data rates in a coverage area to multiple users simultaneously including at cell edges at reasonable cost. Currently, the wireless telecom industry is focused on dense deployment of small cells, the so called ultra-dense networks, to increase spatial reuse of wireless spectrum as the solution for meeting the growing mobile data demand. Dense deployment of small cells requires a large number of backhauls and creates complex inter-cell interference. One solution to the interference problem is to require careful Radio Frequency (RF) measurement and planning and inter-cell coordination, which significantly increases the cost of deployment and reduces the spectral efficiency. Another solution is the Self-Organizing Network (SON) technology, which senses the RF environments, configures the small cells accordingly through interference and transmit (Tx) power management, coordinated transmission and handover. SON reduces the need for careful RF measurement and planning at the cost of increased management overhead and reduced spectral efficiency. The backhaul network to support a large number of small cells is expensive to be laid out.
Another method for increasing spatial re-use of wireless spectrum is MIMO, especially Multi-User MIMO (MU-MIMO). In a wireless communication system, a wireless node with multiple antennas, a Base Station (BS) or a User Equipment (UE), can use beamforming in downlink (DL) or uplink (UL) to increase the Signal-to-Noise Ratio (SNR) or Signal-to-Interference-plus-Noise Ratio (SINR), hence the data rate. MU-MIMO can beamform to multiple UEs simultaneously in a frequency and time block, e.g., a Resource Block (RB), i.e., using spatial multiplexing to provide capacity growth without the need of increasing the bandwidth. Although a MIMO BS with a large number of antennas can extend its DL coverage range through beamforming, the SINR of UEs can decay quickly as the distance between the BS and a UE increases, because UEs far away from the BS have significantly lower SINRs than UEs close to the BS due to large-scale fading, shadowing, and other factors. In addition, the UL range, and hence the UL channel estimation accuracy, is limited by the transmitting power of UEs. Before the BS knows the channels of the UEs, it is unable to perform beamforming. Because of the above disadvantages, the large-scale antenna systems still face the non-uniformity in the coverage of a BS, which degrades users' experience and cannot satisfy the requirement of the next generation network.
Our provisional patent application (PPA) 62/104,086 filed on Jan. 16, 2015 titled “Beamforming in a MU-MIMO Wireless Communication System With Relays” presented inventions using Amplify and Forward Repeater (AFR) to enhance multi-user beamforming systems, in which the AFR is transparent to UEs. Note that in this application, repeaters with embodiments of this invention are referred to as Capacity Projectors (CaPs). FIG. 1 and FIG. 2 show a CaP enhanced centralized system and a CaP enhanced distributed system respectively. PPA 62/104,086 addressed many technical challenges of a wireless network with MU-MIMO and a large number of relays widely distributed over a coverage area, including large number of antennas on the BS and relays, conditions and placement of full-duplex relays, efficient estimation of the total channels, and MU-MIMO beamforming using the total channels. Moreover, it presents significantly more advantageous solutions to dense networks using MU-MIMO and in-band or out-band relays for both sub 6 GHz bands and for cm-wave and millimeter wave (mm-wave) bands. However, it lacks the intelligent control and learning, and active channel shaping capabilities of the present invention.